Electric heater



June 2, 1936. E FI N 2,043,196

ELECTRIC HEATER Original Filed Nov. 11, 1952 Fig.1.

Fig. .2

' mu,,,,,,,,, 7 ll Inventor FT ank E. Finlayson,

ttorney.

Patented June '2 1936 UNlTEDTSTATES PATENT 'oF lcE Frank E. Finlayson,

General Electric New York Pittsfield, Mesa, assignor to Company, a corporation of Original application November 11, 1932., Serial No. 642,256. Divided and this application September 1'7, 1935, Serial No.

- 3 Claims.

My invention relates to electric heaters, and it has for its object the provision of an improved method for sealing the terminals of heaters of this type.

Although not limited thereto, my invention has particular application to incased or sheathed conductor embedded electric heaters of the type wherein a resistance in an insulating material is inclosed by an outer metallic protective casing.

In one of its aspe cts, my invention contem- In accordance with my invention, I place a tubular member, which preferably will be formed of metal, over each terminal of the heater, and provide a fluid impervious joint between the terminal and the tubular member. Surrounding the tubular member is a layer of vitreous material whlch is arranged to make a fluid impervious joint with it. The

vitreous layer is surrounded by a separate casing which has a fluid-impervious joint with the vitreous layer, and also a fluid impervious joint with heater.

This application is invention.

the sheath provided iorthe' a division of my copending 642,256, filed November 11, the same assignee as this For a more complete understanding of this invention, reference should be panying drawing in which Fig.

a sheathed electric had to the accomls is an elevation of heater provided with terminal seals arranged in accordance with this invention;

Fig. 2 is an enlarged fragmentary sectional view of the electric heater of Fig. 1 illustrating a terminal seal arranged in accordance with this invention and used in Fig. 3 is an enlarged the heater of Fig. 1; and fragmentary sectional view of a heater embodying a modified form of this invention.

Referring to the drawing, this invention has larly intended to As shown, the resistance conductor to a'helical coil sheathed of the type described and Patent No. 1,367,341 to 1, 1921, and particube used as an immersion heater. heating unit comprises a helical I0 embedded in a compacted mass of powdered heat refractory insulating material H, the conductor and being incased by a metallic sheath I2. The insulating material H stance, but preferably insulating material may be any suitable subwill be formed or powdered magnesium oxide. This material may be compacted to a hard dense mass having a good heat conductivity in any suitable manner, such as by reducing the diameter of the sheath after the unit has been assembled and the sheath has been loaded with the magnesium oxide. The sheath may be reduced by swaging or rolling.

The resistance conductor l0 extends through a considerabldportion of the length of the sheath l2 and has its two ends connected to terminal members l3 which project iromthe ends of the sheath. While the conductor may be connected to its terminals l3 in any suitable manner, 1 prefer to connect them in the fashion described and claimed in United States Patent No. 1,494,938 to C. C. Abbott, dated May 20, 1924. As there described, the terminal members |3 have their inner ends threaded and are electrically and mechanically connected with the resistance conductor by screwing a number of the end turns of the conductor onto the threaded ends of the. terminals; In this arrangement the terminals may have a diameter slightly larger than the diameter of the helix of the conductor l0. As shown (Figs. 1 and 2), each terminal l3 projects somewhat" from its end of the sheath and is supported at its inner end by the compacted insulating material |I.' N

Heating units of this type can be bent easily into any desired shape. In the immersion heater shown, the heating element is bent substantially in the form of a hairpin. The adjacent ends of the heating element are received by a suitable supporting member M which may be in the form of a plate, or which may be in the form of a threaded plug (as shown) arranged to be received in a threaded aperture provided for it in a wail or supporting plate of a receptacle or 0th device.

A pair of spaced apertures ii are provided in the supporting member H for receiving the two ends of the heating element. As shown, the ends of the heating element are inserted within the passageways l5 so as to project somewhatbeyond the, plate on the opposite side thereof.

As pointed out in detail in my above-mentioned copending application,'suitable fluid impervious joints are effected between the heating elements and its supporting plug ll. As shown, at the points where the ends of the heater enter and emerge from the plug ll, fluid-tightseals are provided which may be formed by brazed joints l6 between the sheath and the plug. For this purpose, the apertures or holes IS in the plug I4 are provided at their ends with recesses which serve to receive suitable brazing material providber ll] which has ing the fluid-tight Joints between the sheath ends and the plug. In order to render the terminals absolutely impervious to the leakage of fluids into the sheath,

I surround each terminal H with a tubular meman internal diameter slightly larger than the diameter to leave a. relatively small annular space between these members. Surrounding this tubular member ll is a substantially homogeneous mass of vitreous material M, such as a high temperature glass arranged to adhere to the tubular member to form a fluid impervious joint with the member. Surrounding the mass of glass i8 is a metallic casing i9 which in turn surrounds the terminal end portion of the sheath, and which is securedto the sheath by a mud-impervious joint 2d. The glass it, the tubular'rnember ll and casing it will have such coeflicients of expansion that the glass will have fluid impervious joints with the tubular member and casing. Between the end of each terminal 53 and its surrounding tubular member M is a suitable fluid-impervious joint 2!.

interposed between the glass seal it and the end oi the sheath l2 and the insulating material it is an insulating washer 22 tormed'oi any suitable electrically insulating material, such as mica. This material increases the insulation between the terminal, 63 and sleeve ll and the sheath 52. Preferably, centrally arranged aperture in the washer will have a diameter substantially equal tothe diameter of the terminal it. i

It will be understood that in making the terminal seal, each terminal sleeve or tubular member ill is arranged in substantially concentric relation with its casing ii). The terminal sleeve H is assembled with the tubular member 1 3 and with a tube (not shown) formed of the glass sealing material 8 t in substantially the same positions relative to each other that they will occupy in the flnished'heater, shown in Fig. 2.

Then the assembly is heated to a temperature at which the-glass becomes soft. The ghsss is then compressed until it completely fills the space between the tubular members H and it so that upon subsequent cooling it will adhere to these members to make fluid impervious joints with them. Preferably, the tubular members l1 and I! will be cleansed before the glass It is applied, as bymeans of sand blasting or suitable machining operations.

The unitary structure comprising the tubular members I! and I9 and the glass I8 adhering to them is then assembled with the heater so that the terminal ll of the heater is received in the tubular member I! and so that the tubular member l8 embraces the terminal end of the sheath.

- Ilhe outside diameter that portion' 01' the sheath which is received by the member I! may be'reduced somewhat, as indicated-in Fig. 2', the internal diameter 01 the member l9 being substantially the same as the diameterot the sheath potrfonto which it is fitted. The tubular member II is sealed to the sheath I! by means of a brazed, soldered or welded fluid impervious joint 20. The end of the tubular member I1 is brazed or otherwise connected with the end oi the terminal [3 so as to form the fluid-tight joint 2|. As shown, the outer .end of the tube I1 is counter-sunk so as to provide a well or cup in which the brazing or soldering material is received. i

of the terminal so .as-

escape, the seal 21, of course, not being formed this tubular member and with the surrounding When the washers 22 are used, they will be threaded over the terminals I 3 before the seals are assembled with the heater.

The tubular member I! performs an important function when the tube I9 is being brazed to 5 the sheath l2. During this process the sheath l2 and tube l9 are heated which causes the air in the sheath to expand. The tubular member 11 provides a path through which this air can at this time. Unless the air were thus permitted to escape, it would tendto bubble out through the brazing material forming the joint 20 which is objectionable.

Instead of being sealed to the sheath by braz- 15 mg, soldering, etc., the tubular member surrounding the glass may have a threaded connection with the sheath so as to provide a fluidtight'joint, as shown inFig. 3. In this arrangement, the terminal sleeve 23, the surrounding tubular member 24 and the glass sealing material 25 between these members are arranged in substantially the same ieshion as are the corresponding elements Ell, it) and it of Fig. 2. In Fig.3, however, the tubular member 24 is pro- 5 vlded with an internal threaded portion 26 arranged to'be screwed on a corresponding threaded portion 21 provided on the terminal end of the sheath. A- suitable sealing compound may be placed on the cooperating threads between the casing 24 and the sheath.

it will be understood that here again the ter-, minal sleeve 23 will beconnccted or joined with the terminal 28 by means of a brazed joint 28.

And here also it is preferable to thread a mica washer 35 over the terminal before the seal is assembled with the heater.

In this heater it is not necessary to vent the sheath when the tube 24 is applied to it, and for this reason, the member 23 need not be in the form of a tube. It may be a solid member having a hole in it for receiving the .terminat and Itis to be understood that it is not necessary I I to use glass for the sealing material ll, 28, but that any other suitable material such at vitreous enamel-maybe used. It is' important, however, that the glass or other sealing material havea high electrical resistance at the operating temperatures' of the terminals.

It will be observed that I have provided a terminal seal which comprises a tubular member I 1, 23 surrounding the terminal of the heater,

, this member in turn being surrounded by a substantially homogeneous layer ll, 25, of glass which makes fluid impervious joints both with casing 22, 24. .The tubularmember ll." surrounding the terminal is Joined with it by means of a fluid impervious joint 21, 28.

Thetermi'nal seals of my invention efl'ectively prevent'the admission of fluids into the sheath. It is to be understood, however, that they may be used just as eii'ectlvely to retain a selected atmosphere in the sheath, such as an atmosphere for preserving the lite or tho-resistance heating element. Thus,

for example. the seals may be used to retain a non-oxidizing or reducing atmosphere in the sheath to protect the heating element.

While I have shown particular embodiments of my invention, it will be understood," 0! course, that I do not wish to be limited thereto since many modifications may be made, and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim asnew and desire to secure by Letters Patent 0! the United States, is:- I 1. The method of sealing the terminal end of an electric heater provided with a resistance conductor, a terminal and a metallic sheath incasing said conductor which comprises placing a metallic tubular member within a second tubular member of larger diameter in substantially concentric relation therewith, filling the space beween said tubular members with a vitreous sealing material, heating said vitreous material to soften it and applying pressure to cause it to adhere to said tubular members, assembling said tubular members to said heater so that said terminal is received within the inner tubular member, and then eflecting a fluid impervious Joint between the outer tubular member and said sheath.

2. The method'ot sealing the terminal end of an electric heater provided with a resistance conductor, a terminal and a metallic sheath incasins'lald conductor which comprises placin: a metallic tubular member within a second tubular member 0! larger diameter in substantially concentric relation therewith, filling the space between said tubular members with glass, heating said glass to soften it and applying pressure to cause it to adhere to said tubular members, assembling said tubular members to said heater so that said terminal is received within the inner tubular member, and then brazing said outer tubular member to aid sheath and said inner tubular member to said terminal.

3. The method of sealing the terminal end or an electric heater provided with a resistance conductor. a terminal and a metallic sheath incasins said conductor metallic tubular member within a second tubular member of larger diameter in substantially concentric relatim therewith, iilling the space hetweensaid tubular members with glass, heating said glass to soften it and applying pressure to cause it to adhere to said tubular members, assembling said tubular members to said heater so that said terminal is received within the inner tubular member, threading said outer tubular member on said sheath seas to eflect a fluid-tight Joint between said members and then brazing said inner tubular member to said terminal.

mm; 1:. i mLAYsoN. 9

which comprises placing. a 

